1. Field of the Invention
This invention generally relates to a fuse structure for a semiconductor device, and more particularly to a fuse structure having at least a heat buffer block for a semiconductor device.
2. Description of Related Art
As the size of a semiconductor device becomes smaller, the semiconductor device is more seriously affected due to impurity or defect in itself. A defect of a single diode or transistor may cause the whole chip to fail. To solve this problem, some redundant circuits connected to fuses generally will be added into the circuit. When a defect is found in a circuit, the fuses can be used to disable the defected circuit and enable the redundant circuit. For memory devices, the defected cell can be replaced by a non-defected cell to its address. Another reason to use fuses in the integrated circuits is to permanently write the controlling bytes such as ID codes into the chip.
Generally, the fuses are made of polysilicon or metal. Laser fuses and electronic fuses are two major types of fuses based on how the fuses are blown to be open. The laser fuses will be blown by the laser beam; and the electronic fuses will be blown by currents. The electronic fuses are generally applied to EEPROM devices, while the laser fuses are generally applied to DRAM devices.
Generally, an integrated circuit has a passivation layer including silicon nitride, silicon oxide or both at the top thereof. For the layout of the laser fuse, to prevent the passivation layer from damage, an opening at the top layer is required and the laser beam has to precisely focus on the fuse in order not to damage the adjacent devices. However, it is common that the passivation layers neighboring to the fuses are damaged due to the strong power of the laser beam.
For the layout of the electronic polysilicon fuse, it requires a high voltage to generate a current big enough to heat the fuse to rupture the fuse. When the size is getting smaller, the voltage that the integrated circuit can provide is decreased. Hence, a silicide layer is disposed on the (polysilicon) fuse so that an appropriate voltage can blow the fuse. Since the heat generated by the current can enhance the electron migration, the silicide layer and the polysilicon fuse will agglomerate together to make the silicide layer rupture and the grains of the polysilicon re-grow.
To make the fuse open means either the fuse is ruptured, the silicide layer on the polysilicon fuse is fused, or the post-burn resistance of the polysilicon fuse is so high to deem open.
As the conditions of the manufacturing process and the applied voltage frequently change, even after applying the voltage to blow the fuse, the remaining fuse may be found or the post-burn resistance is not stable, which affects the reliability and the performance of the devices. Further, the heat generated by the current my also deteriorates the adjacent devices and affects their reliability.